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Letter Drill Q = .332I guess 21/64 or 11/32. Probably 21/64 since it's a tapered tap anyway.Excellent resource:http://catalog.starrett.com/catalog/...30801&Mode=REFI used to have these pinned up all over my shop, but now I've got an even better chart that cross-references them all. EDIT: Slow... so slowww...

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Sounds like you folks are quoting from the NPTF (Dry Seal) column not the NPT column. But I really think we're splitting hairs since it's really gonna depend on how much he runs that tap in.Dammit, is it just me, Starrett and my Busy Bee Tools poster that agree on that?

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Several charts I have refered to list the letter drill R for 1/8" 27 National tapered pipe thread.I found one that listed the letter drill Q. I agree , between the two sizes is splitting hairs when it comes to decimal size and the criticality of tapping a hole to recieve a 1/8" NPT nipple.

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This is a little off topic but I've always wondered why the world cannot agree on one standard for threads & bolt sizes.Or should that read why can't the US use the same standard as the rest of the world.

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We was wondering why the rest of the world doesn't use our national standard. Actually the USA now incorporates all standards of thread sizes and has for years.Just that our original national standards are still one of the standards.Sorta like gallons and litres.Or is that liters? Besides ,metric bolts in my Evinrude just wouldn't be right.

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but the brits have a pipe size as well it also depends on the materiel to be tapped and whether or not its a tapered,sealing, or straight,non-sealing pipe joint. the shift cable in the merc bell housings are modified from fwd entry to aft entry with a 1/4-14 straight NPT. I also use it to chase the threads after I have to drill out the snapped off cable. there is a book about 200 pages long describing thread sizes and standards, I machined class 3 threads for mny years as well as metric,buttress,acme,stub acme, pipe and a host of other oddball stuff.

no tech questions by PM, they wont get answered.
you have to be trusted by the people that you lie to .